| Summary: | 博士 === 臺灣大學 === 土木工程學研究所 === 98 === This study applies the subspace identification to system identification and damage detection. Many of the damage detection methods are surveyed in order to establish a continuous monitoring system of the civil engineering structures. First, according to the use of the collection data two theoretical derivations are introduced: (1) the stochastic subspace identification (SSI) using output-only data, or the ambient vibration data for continuous monitoring; and (2) the subspace identification (SI) using input/output data, or the seismic responses. The user-defined parameters in the subspace identification are studied through the laboratory and field tests and also three noise-rid methods are employed to distinguish the noise modes from the results of analysis. For damage detection three methods are introduced: (1) null subspace-based damage detection; (2) inverse methods for the identification of the normalized stiffness and damping matrices; and (3) two-stage finite element model updating. These methods can accurately detect the location or quantification of the structural damage from the results of identification. For the purpose of continuous monitoring, in this study a new technique for updating LQ decomposition is proposed to achieve the recursive computation of the subspace identification. From the results of the numerical simulation and the laboratory experiment it is proven that the proposed method of the recursive subspace identification can accurately detect the abrupt damage of the structure. Finally, the proposed methods are applied to the long-term monitoring of the new Civil Engineering Department Research Building in the campus of National Taiwan University, which is a mid-story isolation building. The relationship between the natural frequencies and the drift of the isolation system is established to provide a reference for future research.
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